Electronic structure of copper phthalocyanine from G0W0 calculations

We present all-electron G(0)W(0) calculations for the electronic structure of the organic semiconductor copper phthalocyanine, based on semilocal and hybrid density-functional theory (DFT) starting points. We show that G(0)W(0) calculations improve the quantitative agreement with high resolution photoemission and inverse photoemission experiments. However, the extent of the improvement provided by G(0)W(0) depends significantly on the choice of the underlying DFT functional, with the hybrid functional serving as a much better starting point than the semilocal one. In particular, strong starting-point dependence is observed in the energy positions of highly localized molecular orbitals. This is attributed to self-interaction errors (SIE), due to which the orbitals obtained from semilocal DFT do not approximate the quasi-particle (QP) orbitals as well as those obtained from hybrid DFT. Our findings establish the viability of the G(0)W(0) approach for describing the electronic structure of metal-organic systems, given a judiciously chosen DFT-based starting point.